AFTER PUTTING A NEW CHAIN ON THE #2P-101A SCREW SPROCKET, EE WAS INSTALLING THE GUARD OVER THE CHAIN & SPROCKET & HE WAS BENT OVER SLIGHTLY BECAUSE THERE IS AN I BEAM 12"" ABOVE THE GUARD & WH ILE HE WAS TIGHTENING THE BOLTS ON THE GUARD HE WAS IN AN AWKWARD POSITION WHICH CAUSED HIM TO STRAIN HIS LOWER BACK